C - Add an element to a struct pointer

Question

Im trying to add aa struct Song to my struct pointer song* but when trying to write it to a file it just gives out junk. This is my function:

void addSong(Song *song, char songName[], char artistName[], int publicationYear, int *nrOfSongs)
{
    Song *tempSongs = (Song*)malloc(sizeof(Song)*(*nrOfSongs));

    for (int i = 0; i < (*nrOfSongs); i++)
        {
            strcpy(tempSongs[i].artistName, song[i].artistName);
            strcpy(tempSongs[i].songName, song[i].songName);
            tempSongs[i].publicationYear = song[i].publicationYear;
        }

    free(song);
    *nrOfSongs = (*nrOfSongs) + 1;
    song = (Song*)malloc(sizeof(Song)*(*nrOfSongs));


    for (int i = 0; i < ((*nrOfSongs)-1); i++)
        {
            strcpy(song[i].artistName, tempSongs[i].artistName);
            strcpy(song[i].songName, tempSongs[i].songName);
            song[i].publicationYear = tempSongs[i].publicationYear;
        }
}

Edit 1: Sorry for the bad question.

My function writeToFile:

void writeToFile(char fileName[], Song *song, int *nrOfSongs)
{
    char name[256];
    snprintf(name, sizeof(name), "%s.txt", fileName);
    FILE * file = fopen(name, "w");

    fprintf(file, "%d", *nrOfSongs);
    fputc('\n', file);

    for (int i = 0; i < (*nrOfSongs); i++)
    {
        fputs(song[i].songName, file);
        fputs(song[i].artistName, file);
        fprintf(file, "%d", song[i].publicationYear);
        fputc('\n', file);
    }

    fclose(file);
}

An example of a file:

4
Mr Tambourine Man
Bob Dylan
1965
Dead Ringer for Love
Meat Loaf
1981
Euphoria
Loreen
2012
Love Me Now
John Legend
2016

I want to add a song and by that i want to add an artistName, songName and publicationYear to my struct pointer and then write the struct pointer to a new file.

Answer 1

Instead of copying over arrays twice, you should enlarge the array song using realloc() , and just add the new element to it, like so:

Song *addSong(Song *song, char songName[], char artistName[], int publicationYear, int *nrOfSongs) {
  *nrOfSongs++;
  song = realloc(song, *nrOfSongs * sizeof *song);
  // Don't forget to do error checking here, realloc() may return NULL

  strcpy(song[*nrOfSongs - 1].artistName, artistName);
  // et cetera

  return song;
}

Because you are reallocating the memory, the pointer to the array changes, so you have to return the new pointer to the caller, like @wildplasser says.

Also, strcpy() is an unsafe function. Consider using a safer alternative, like snprintf() .